Syphilis RPR (rapid plasma reagin)
A blood screening test for syphilis, a sexually transmitted infection caused by the bacterium Treponema pallidum. A reactive result is reported with a titre (a strength) and is always confirmed with a second, specific test; the titre is then used to follow whether treatment is working.
What it measures
The RPR (and the closely related VDRL) is a 'non-treponemal' screening test for syphilis, an infection caused by the bacterium Treponema pallidum. It does not detect the bacterium directly; instead it detects antibodies the body makes against material released from damaged cells during infection. A reactive (positive) result is reported with a titre — a dilution such as 1:8 or 1:32 — that reflects how active the infection is. Because the test can occasionally react for other reasons (pregnancy, some autoimmune conditions, other infections), a reactive RPR is always confirmed with a specific 'treponemal' test (such as TPPA or a treponemal antibody assay) that targets the bacterium itself. The RPR's great strength is that its titre falls with successful treatment, so it is the standard way to confirm a cure and to detect re-infection: a four-fold drop (for example 1:32 to 1:8) after treatment indicates a good response. Syphilis is important to catch because, untreated, it progresses through stages and can affect the heart, brain and nerves years later, and it can be passed to a baby in pregnancy.
What a high value can mean
- A reactive result — screens positive for syphilis; must be confirmed with a specific treponemal test.
- A high or rising titre — suggests active or recent infection, or re-infection.
- A false-positive reaction — occasionally from pregnancy, autoimmune conditions (such as lupus) or other infections; the confirmatory test sorts this out.
- A persistent low titre after treatment — a 'serofast' state that can remain in some people.
What a low value can mean
- Non-reactive (negative) — the expected result; no antibodies detected.
- A falling titre after treatment — a four-fold drop indicates the treatment has worked.
- Very early infection — the test can be non-reactive in the first days of a primary sore, so it may be repeated.
When to discuss with a doctor
A syphilis RPR is used to screen for and monitor syphilis — as part of routine sexual-health checks, in pregnancy, and when symptoms such as a painless sore, a rash on the palms and soles, or unexplained signs suggest it. A reactive result needs a confirmatory treponemal test and, if confirmed, treatment (usually penicillin) and screening for other sexually transmitted infections including HIV. The titre is then followed over time to confirm the treatment worked. Because syphilis is fully curable when caught but serious if left, a reactive result should always be acted on with a clinician, and sexual partners will need testing. Mediora.AI shows the RPR result and titre alongside related infection screens so the picture is read together; diagnosis, confirmation and treatment belong with your doctor or a sexual-health service.